In recent years, flip-chip bonding techniques have increasingly been used to connect (bond) integrated circuit (IC) chips to interconnection substrates and to package substrates. In flip-chip bonding an IC chip component to an interconnection component such as ceramic interconnection substrate, a plurality (e.g., an array) of solder balls (also called “solder bumps”) is formed on a face of a component, typically the IC chip component, and the bumped component is brought into a face-to-face relationship with the other component. The two components are then heated (such as in a furnace) to reflow (heat, then allow to cool) the solder bumps, thereby making electrical connections between respective terminals of the two components.
A “captured cell” technique is described in the '652 Patent. For example, FIG. 1 of the '652 Patent, reproduced as FIG. 1 herein, illustrates a technique 100 for forming solder balls on a surface of a substrate 102. The substrate 102 has number of pads 104 on its top (as viewed) surface. The pads 104 are typically arranged in an array, having a pitch (center-to-center spacing from one another). The substrate 102 is disposed atop a heater stage 106. A mask (stencil) 110 is provided. The mask 110 is a thin planar sheet of relatively stiff material, such as molybdenum, having a plurality of openings (cells) 112, each corresponding to a pad 104 whereupon it is desired to form a solder ball on the substrate 102. The mask 110 is placed on the top (as viewed) surface of the substrate 102 with the cells 112 aligned over the pads 104. The cells 112 in the mask 110 are filled with solder material 114. This is done in any suitable manner such as by smearing solder material on the top (as viewed) surface of the mask 110 and squeegee-ing the solder material 114 into the cells 112 of the mask 110. A pressure plate 120 is disposed onto the top (as viewed) surface of the mask 110. This holds the mask 110 down onto the substrate 102, and the substrate 102 down onto the heater stage 106. This also closes off the cells 112—hence, the terminology “captured cell”. The heater stage 106 is heated up, typically gradually, to a temperature sufficient to cause the solder material in the cells 112 to melt (reflow). When the solder material melts, the individual solder particles will merge (flow) together and, due to surface tension, will try to form (and, typically, will form) a sphere. When the solder material re-solidifies, it assumes a general spherical or hemispherical shape. The mask 110 is then removed from the substrate 102.
A mechanism for shuttling a mask from a printing station to a product being ball bumped is described in the '652 Patent. For example, FIG. 10 of the '652 Patent, reproduced as FIG. 2 herein, illustrates an exemplary ball bumping machine 1000 having a base 202, a chuck 204 on the left side for holding a wafer 206 and a heater stage 208 on the right side. A mask 210 is held in a frame 212. The chuck 204 is disposed in chuck base 214. The heater stage 208 is disposed in a heater stage base 216. An elongate shuttle (carriage) mechanism 218 is pivotally attached to the base 202 at a point “P” between the chuck 204 and the heater stage 208. The frame 212 is held in a carrier 220 which is attached to the opposite (free) end of the shuttle mechanism 218. A motor 221 controls the position of the shuttle mechanism 218. The shuttle mechanism 218 can shuttle the mask 210 (i.e., the carrier 220) between the heater stage 208 on the right side (as shown) and the chuck 204 on the left side. The shuttle mechanism 216 pivots about the point “P”. Cameras (not shown) are used to make alignments, for example of the mask 210 to the wafer 206. A set of holddown magnets 222, which preferably are electromagnets, selectively hold the chuck base 214 to the machine base 202. Similarly, a set of holddown magnets 222, which preferably are electromagnets, selectively hold the heater stage base 216 to the machine base 202. The carrier 220 is ferrous, or has ferrous “lands”. A set of lift magnets 226, which preferably are electromagnets, selectively hold the carrier 220 to the heater stage base 216. Similarly, a set of lift magnets 228, which preferably are electromagnets, selectively hold the carrier 220 to the chuck base 214. In this manner, the mask can be brought down onto the heater stage, the magnets 226 turned on, the magnets 224 turned off, and the heater stage can be lifted by the shuttle mechanism 216. In other words, when the mask is shuttled, it can take the heater stage with it. Similarly, the mask can be brought down onto the chuck, the magnets 228 turned on, the magnets 222 turned off, and the chuck can be lifted by the shuttle mechanism 216.